Hi Theoldun, thanks for your reply
I really do appreciate your help and feedback on this, spent most of the weekend trying to work out alternatives for the uvalues and my brain is now fried.
The extension is two-storey which comes off the rear of the existing cottage with a pitched roof (with two dormer windows).
Our house is electric-only so think we would benefit from extra insulation but maybe just a few points below the maximum uvalue would do just fine.
External size is: 6.75 x 5.7m
Cavity walls: our spec said 120m cavity with 65mm celotex and the rest as air space. Problem with this is the brickie has already laid up to damp as he is away for the next few weeks, so we've got to stick with 120mm but not sure how to fill it!? We have got brick outer leaf and thermalite innerleaf with plasterboard (dot dab) internal. I can see from LABC that maximum is 0.28, our spec is suggesting 0.19.
Ground floor slab: I've worked out p/a to be 0.5.
LABC says max uvalue 0.22 and our spec says 0.20 to include the following:
150mm slab on 500 gauge VPL on 70mm Celotex FR5000 on 1200 gauge DPM on 25mm sand blinding on 200mm well compacted hardcore. The insulation depth is as you suggest (albeit the more expensive product) - does the hardcore etc sound about the right depths?
Roof: warm deck pitched roof. LABC says 0.18 and our spec says 0.13 at rafters and 0.14 at ceiling to include - Nilvent breather membrane, 150mm FR5000 celotex between rafters plus GD5040 celotex 40mm under rafters
Ceiling is FR5000 120mm between joists and FR5000 60mm across joists. This seems an awful lot to me!!
Thanks in advance for any help/advice!
I really do appreciate your help and feedback on this, spent most of the weekend trying to work out alternatives for the uvalues and my brain is now fried.
The extension is two-storey which comes off the rear of the existing cottage with a pitched roof (with two dormer windows).
Our house is electric-only so think we would benefit from extra insulation but maybe just a few points below the maximum uvalue would do just fine.
External size is: 6.75 x 5.7m
Cavity walls: our spec said 120m cavity with 65mm celotex and the rest as air space. Problem with this is the brickie has already laid up to damp as he is away for the next few weeks, so we've got to stick with 120mm but not sure how to fill it!? We have got brick outer leaf and thermalite innerleaf with plasterboard (dot dab) internal. I can see from LABC that maximum is 0.28, our spec is suggesting 0.19.
Ground floor slab: I've worked out p/a to be 0.5.
LABC says max uvalue 0.22 and our spec says 0.20 to include the following:
150mm slab on 500 gauge VPL on 70mm Celotex FR5000 on 1200 gauge DPM on 25mm sand blinding on 200mm well compacted hardcore. The insulation depth is as you suggest (albeit the more expensive product) - does the hardcore etc sound about the right depths?
Roof: warm deck pitched roof. LABC says 0.18 and our spec says 0.13 at rafters and 0.14 at ceiling to include - Nilvent breather membrane, 150mm FR5000 celotex between rafters plus GD5040 celotex 40mm under rafters
Ceiling is FR5000 120mm between joists and FR5000 60mm across joists. This seems an awful lot to me!!
Thanks in advance for any help/advice!